The present invention relates to a device for adjusting pressure applied to a varnishing cylinder of a machine for varnishing in which workpieces are movable between a varnishing cylinder, having a shell formed of a rubber or any other elastic material, and a hard pressure cylinder, with the adjusting device including a first adjusting unit for adjusting the pressure between the varnishing and the pressure cylinders and a second adjusting unit for adjusting the pressure between the varnishing cylinder and a varnish feed roller of a varnishing unit.
Such varnishing machines are used, e.g., in manufacturing of drink cans, glass caps, or crown caps, where the workpieces, before being pressed, are covered with inner and outer varnish layer and, after pressing operation, with a protective varnish layer. The applied varnish should meet specific requirement so that it would not crack when the workpieces are subsequently subjected to stamping and deep-drawing.
In the old varnishing machine, varnish was just poured over a workpiece. The modern varnishing machines are designed with an object of insuring as economical use of varnish as possible. Therefore, often, the varnishing cylinders, which are adjusted for varnishing of surfaces in which blank areas need be provided, are fitted with exactly positioned cutouts or grooves. The advantage of the varnishing cylinders designed for varnishing of the entire surface of a workpiece consists in that they can be regrinded several times and, therefore, have an extended service life. However, due to the decrease of the diameter of the varnishing cylinder, which results from regrinding, the rotational speed of the varnishing cylinder need be adjusted. The adjustment of the rotational speed of the varnishing cylinder, to a lesser extent, is needed because of the soaking of the varnishing cylinder shell. Further, an exact adjustment of the pressure between the varnishing and pressure cylinders is necessary for obtaining of an extremely thin and, at the time, of a highly uniform varnish coating.
A varnishing machine with an adjusting device for adjusting the pressure between the varnishing and pressure cylinders and between the varnishing cylinder and the varnish feed roller is known. In this varnishing machine, the driving of the varnishing cylinder is effected by a pressure air-actuated slip clutch which enables a very fine control of the rotational speed of the varnishing cylinder during the operation of the varnishing machine. However, the control of the rotational speed requires participation of the operator. For effecting varnishing of surfaces with blank area, an electrical controller is used which monitors the adjustment of the varnishing cylinder. After the disconnection for adjusting purposes, a change lever is used for adjusting three operational conditions. Altogether, the following adjustment are important for a proper operation of the varnishing machine, namely, the adjustment of the varnishing cylinder and the varnish feed roller, the adjustment of all of the rollers, providing for their positioning parallel to each other, metering of the necessary amount of varnish. To this end, manually operating spindles are used. After effecting the necessary adjustments necessary for a particular operational condition, the varnishing cylinder and the varnish feed roller are fixed to the machine frame without any play. However, with these adjustments, a non-uniform contact pressure along the generatrix of the varnishing cylinder shell may occur, which, leads eventually to operating errors, and a desired reliability of the operation cannot be achieved.
Accordingly, an object of the invention is a pressure adjusting device for a varnishing machine of the above-described type which would insure obtaining of an extremely thin and highly uniform varnish coating.
Another object of the invention is a varnishing machine in which the adjustment of pressure between the varnishing and pressure cylinders and the varnishing cylinder and the varnish feed roller is effected automatically.